I've been thinkng about this myself. Right now I have a audio line-level connection bewteen the PC in the family room and the receiver in the entertainment center in the living room (about a 50' run using quad-shield coax for each of the two channels). The only problem with this is that I can only control volume in the living room but can't skip tracks, etc. without going back to the PC.
I'm thinking about getting a video card with TV out and running a video line from the PC to the entertainment center. Add to that an ATI wireless remote for the PC, and I could display the pc screen on the tv and control the whole deal from the living room using the full functionality of MC9. The only problem is that I'd have to resize the PC display res to be able to read genre/artist/album info on the TV because of the TV's low resolution. I guess if I had an HDTV that wouldn't be a problem.
I like the idea of the wireless systems like the Pinnacle, but they make you use their own software, not something I am interested in.